The latest potential alternative to the traditional gasoline engine touted for the auto industry — plug-in hybrids and their lithium-ion batteries — might not change what most people drive anytime soon.

Among those cautious about the potential for both is a company that should know — Toyota Motor Corp., the world's largest producer of hybrids.

Toyota will introduce two new hybrids in January at the Detroit Auto Show, and both will use the tried and true nickel-metal-hydride battery that helps power the Prius. Neither will be a plug-in, whose batteries can be recharged in a household outlet.

Still, the race is on to develop the lighter, more powerful lithium-ion batteries, despite obstacles including cost and safety concerns, said experts at a recent conference in Chicago.

Lithium-ion batteries have exploded and caught fire in laptop computers, and they're four to five times more expensive than others.

Calling electric-based vehicles ''the only sustainable solution'' for the auto industry, Said Al-Hallaj, head of renewable energy programs at the Illinois Institute of Technology, acknowledges that safety concerns are real. ''We don't want to make the front page for the wrong reasons. Let's step back and do it correctly.''

General Motors Corp. and Toyota have announced plans to introduce plug-in hybrids in 2010, and both will use the lithium-ion batteries more suited to them.

GM, which just this month gave the plug-in Chevy Volt the final go-ahead, said it will have a range of 40 miles on electric power, so motorists who drive less than that between charges won't use any gas. After the batteries drain, the Volt's gasoline engine recharges them, adding another 600 or so miles to its range.

GM says it has overcome the safety issue with a lithium-ion chemistry that avoids the high temperatures that led to explosions.

Automakers also are experimenting with fuel-cell vehicles that use hydrogen to generate electrical power, but so far have only built small test fleets. Analysts doubt that fuel-cell vehicles will be sold in volume before 2015 at least because there are few hydrogen filling stations and the cars currently cost more than $100,000 to build.

Toyota hasn't identified its plug-in, though analysts expect it will be a version of the Prius. Spokesman John Hanson dismissed safety concerns by saying, ''We're not going to put out a battery that's going to catch fire. We think that is probably easily solved.''

But the cost of the batteries is an issue at Toyota. Hanson would say only that the automaker expects them to cost more than the roughly $3,000 to replace the nickel-metal-hydride batteries in the Prius.

But Paul Boskovitch, chief engineer of hybrid systems for auto supplier Ricardo Inc., ventures that lithium-ion batteries needed to power a vehicle now run $10,000 to $15,000, which would make such a vehicle price prohibitive.

Prius' success — more than 1 million sold worldwide and 277,000 in the U.S. — also gives Toyota little reason to go full-tilt to plug-ins. The sophisticated hybrid system in the Prius operates seamlessly to recharge the batteries while driving.

The plug-in Toyota is working on will have a range of 10 to 15 miles on electric only and then operate like the Prius.

And while GM intends to mass-produce the Volt from the outset, Toyota will start by leasing a few hundred plug-ins to fleet customers.

Ford Motor Co. also is being deliberate with lithium-ion technology, testing 20 plug-in Escape Hybrids before deciding to go to wider production.